Lead-in bushings



Jan. 13, 1959 F J. CQREY 2,868,868

LEAD-IN BUSHINGS Filed April 26, 1957 @WWW v TTOR/EY United StatesPatent Manufacturing Company, Waltham, Mass., a corporan tion ofDelaware Application April 2 6, 1957, Serial No. 655,220

31 Claims. (Cl. 174-153) This invention relates to a lead-in bushing,and, more particularly, to a bushing for providing a high electricalinsulation and a hermetic seal to a terminal or other conducting memberat its point of entry into a case container -or similar housing. f

lIn many types of electrical apparatus, for example, transformers, it isdesirable and even necessary to enclose some element, such as a coil, ina housing. Frequently, the housing must be hermetically sealed toprevent the loss of fluid filling, such as oil, from the container or toprevent the entrance into the interior of air or moisture from theatmosphere. The lead-in connections for such apparatus must be wellinsulated from the metallic walls through which they pass, while at thesame time the opening must be sealed against leakage even atconsiderable difference in pressure between the interior and theexterior of the container.

This has been done by means of Ia resilient insulating bushingconstructed in tw-o parts, one tting inside of the other with a centralopening through both pieces in which the conductor is mounted. Thepieces can be held together by means of an eyelet that is somewhatlonger than the bushing and is forced into the assembled bushing againsta shoulder formed on the central conductor which results in crimping theouter end of the eyelet against the walls of the opening in the bushingto hold the parts together. With such a bushing, when used with apotting compound, the potting compound may shrink away from thematerials from which the bushing is formed, leaving a void spaceIbetween the metallic eyelet and the metallic case. With suii'icientpotential diierence, there may be a breakdown between the eyelet orcentral conductor and the metallic case. When this type of terminal isused with yoil-filled units, the oil of .the filling tends to `beabsorbed by the resilient ,plastic of the bus-hing, causing it to swelland destroy the seal.

By the construction of the invention, a cup-shaped washer of insulatingmaterial is mounted between the inner end of the bushing and the eyelethead. Where it is desired to prevent electrical breakdown through anyvoid left between the shrinking potting material and the bushing, thewasher is mounted with the lip pointed inward to present a longerleakage path to theelectrical potential. In this embodiment the washe-ris'made of a material to which the potting compound will adhere,preventing the formation of a void in this region. Where it is desiredto limit the Iabsorption of an oil filling by the resilient plastic orrubber bushing, the cup-shaped Washer is mounted with its lip pointedoutward toward the metallic casing to enclose the plastic parts of thewasher and prevent the swelling of these parts Vby the absorption of theiiller iiuid. ln this embodiment of the invention, the washer is made ofoil-resistant material.

The foregoing and other advantages, objects and features of theinvention will be better understood from the following description takenin conjunction with the accompanying drawing wherein: v I

2,868,868 Patented Jan. 1 3, 1959 rice `Fig. l is an exploded view ofthe bushing of the invention', f

fFig. 2 is a longitudinal sectional lview of an assembled embodiment ofthe invention; and

Fig. `3 is a longitudinal sectional view of another assembled embodimentof the inventio-n.

=In the drawing, reference numeral 10 designates an electrical conductorwhich extends through an axial opening in a two-part bushing made ofresilientinsulating material such as rubber or tetrafluoroethylene(Teflon).consisting ot' a male part 11 dimensioned for mating fitk in anopening into a fem-ale part 12. An eyelet13 passes through an opening ina cup-shaped washer 1.4 made. of insulating material suchv as fibersheet. and `the opening inthe bushing dimensioned for interference titwith it. The conductor 10 is inserted into the eyelet, the insidediameter of which is dimensioned for press t with it, and the eyelet isforced against a shoulder 15 formed on the conductor 10, causing theeyelet to be crimped in the region 16 near its outer end, as best seenin Figs. 2 and 3. The two parts 11 and 12 of the bushing are positionedon either side of the mounting case or partition 17. The resilientmaterial of the lbushing is compressed within an opening 18 in the case17, and swells out beyond it to form a tight tit. When the bushing isused with a component having a case tilled with potting cornpound 20 ofa type that does not adhere to the material of the bushing, a slightvoid 21 will `be left about the male part 11 of the bushing throughwhich there can be an arc-over between the case 17 and the conductor lo,or eyelet 13. By mounting the cup 1-4 made Iof insulating material withits lips 22 extending inward, as shown in Fig. 2, the leakage path forthis breakdown is made longer all around the lip 22 of the washer 14, sothat an arc-over is less likely t-o occur. When the bushing is used witha cas-e 17 lled with insulating oil, or other 4material that is llikelyto be absorbed by the bushing, causing it to swell and possibly pullaway from the eyelet or the case, breaking the seal, the cup 14 can bemounted with its lip 22 extending outward, as shown in Fig. 3. Thisconstruction compresses the bushing and prevents it from swelling awayfrom the opening in the case to `leave a Ibreak in the seal. Thus thisconstruction protects the seal.

The construction of this invention provides a compact, cheap lead-in`bushing for encased components that is protected from electricalbreakdown and leakage of the hermetic seal.

This `invention is not limited to the particular details ofconstruction, materials and processes described, as many equivalentswill suggest themselves to those skilled in the art. It is accordinglydesired that the appended claims lbe given a Ibroad interpretation`commensurate with the scope of the invention within the art.

What is claimed is:

1. A lead-in bus-hing mounted in an opening in a conductive casecomprising a member of two resi-lient in sulating parts one on eitherside of the case one fitting in an opening in the other, each having apassage extending longitudinally therethrough, an eyelet dimensioned forinterference t with said passage, an electrical conductor dimensionedfor force tit in said eye-let and formed with a shoulder near one end,and a cup-shaped washer of insulating material mounted at the inner endof said bushing, said eyelet being crimped against the shoulder formedon the conductor and outward against the outer resilient insulatingmember, to fasten said bushing, said conductor and said washer togetherin the 'opening in the conductive case. e

2. A lead-in bushing mounted in an opening in a conductive casecomprising a member of two resilient insulating parts one on either sideof the case one tting in an opening in the other, each having a passageextending longitudinally therethrough, an eyelet dimensioned forinterference t with said passage, an electrical conductor dimensionedfor force t in said eyelet and formed with a shoulder near one end, vanda cup-shaped Washer of insulating material mounted at the inner end ofsaid bushing opening inward, said eyelet being crimped against theshoulder formed on the conductor and outward against the outer resilientinsulating member to fasten said bushing, said conductor and said washertogether in the opening in the conductive case,

3. A lead-in bushing mounted in anfopening in a conductive casecomprising a member of two resilient insulating parts one on either sideof the case one fitting in an opening in the other, each having apassage extending longitudinally therethrough, yan eyelet dimensoned forinterference t with said passage, and an electrical conductordimensioned for force t in said eyelet and formed with a shoulder nearone end, and a cupshaped washer of insulating material mounted at theinner end of said bushing opening `outward, said eyelet being crimpedagainst the shoulder formed on the conductor and outward against theouter resilient insulating member to fasten said bushing, said conductorand said washer together in the opening in the conductive case.

References Cited in the le of this patent UNITED STATES PATENTS2,195,029 Hathorn Mar. 26, 1940 2,647,432 Huck Aug. 4, 1953 2,682,570Elliott June 29, 1954 2,816,950 Kruss et al Dec. 17, 1957 FOREIGNPATENTS 953,892 France May 30, 1949 511,447 Canada Mar. 29, 19,55

